A. Field of the Invention
This invention relates generally to a centralized control apparatus for use in conjunction with a plurality of data processing systems and a plurality of shared and non-shared peripheral subsystems. In particular, a unit is provided which is able to control one or more system's accessibility to one or more peripheral subsystems from a central location. This unit has the capability of either allowing a peripheral subsystem to be concurrently accessed by more than one data processing system or ensuring that the peripheral subsystem is exclusively accessible to one one data processing system.
B. Prior Art
In the past, as a customer's need for data processing capability increased, the customer was required to either replace his existing system with a larger system or alternatively to add further systems to operate in conjunction with his existing one. Because of the numerous difficulties inherent in either solution, the customer often either delayed his decision until the last possible moment or he attempted to do without the expansion altogether. In other words, there was little or no flexibility in his existing system.
Even with the advent of large scale multiprocessing systems or with the increasing use of multiple similar systems, there was an increasing need for flexibility in the manner of use of each system component or set of system components.
It is often advantageous to be able to separate a multiprocessor system into two or more electrically isolated and software independent entities. Each of these entities, of course, has the complete characteristics of a full operational system. One such entity might be required for maintenance purposes, while the other is used for work applicable to its site. Or there may exist the need for two user programs to be running concurrently, one performing scheduled production work while the other is dedicated to highly sensitive data processing that requires complete electrical isolation from the first for reasons of security.
The capability of forming electrically isolated and software independent entities in a given multiprocessor system from a central location has been achieved. Further, changing the composition of the independent entities within a system, by adding or removing components, without disrupting normal operations has also been achieved. Although the peripheral subsystems could be uniquely associated with a particular independent entity and electrically isolated from the others, the control of their association was either manual or via software functions associated with each independent entity. In the latter case, there was no dynamic hardware means to prevent the software of one independent entity from causing the removal of a subsystem from another entity and subsequently adding the subsystem to the first entity. In particular, dynamic hardware protection of mass storage files from a multiplicity of entities having a hardware means of communication with them was not available. Additionally, the capability of adding or removing a subsystem to or from entities was limited to entities within a single system. For example, a peripheral subsystem such as a card reader may have limited use as a single subsystem, however, if a customer site had multiple systems then the subsystem's utilization would be considerably increased if it could be used by each of the multiple systems. Naturally, the cost of any additional subsystems also could be spread over all of the systems using it and its increased utilization would likewise reduce its unit cost.
Most peripheral subsystems of present day data processing systems have interfaces capable of communication with more than one input/output processor.
However, in all of such known systems, these interfaces were fixed in a certain inflexible mode, either electrically or manually, upon determination of a particular system configuration. Thereafter they were only changed if the particular predetermined system configuration was modified and a change was necessary to accommodate the modification.
It is the purpose of this invention to provide a peripheral subsystem access unit which possesses increased interface flexibiity, in that it is not limited in its utilization to one system nor to one configuration.